1. Field of the Invention
This invention relates to the field of integrated circuit (I.C.) leadframes, and particularly to leadframes designed to provide improved heat dissipation.
2. Description of the Related Art
A I.C. package's "leadframe" typically includes the leads that extend from the package, the structure that supports the I.C. die, and any structures employed to hold these elements together. Many types of leadframes have been developed and are in use, including "lead-on-chip" (LOC) and "chip-on-lead" (COL) leadframes, for example.
A standard 16-lead "thin shrink small outline package" (TSSOP) leadframe is shown in FIG. 1. An I.C. die 10 is on a "paddle" 12, and is secured to the paddle with some type of adhesive 14. The ends of the package's leads 16 which are to be connected to the die are placed near, but physically separate from the die, and the interconnections between the die and the leads are provided by wire bonds 18. The ends of the leads nearest the die are referred to herein as the "inner" portions of the leads, with the opposite ends referred to as the "outer" portions.
When operating, an I.C. die generates heat, and many leadframes include features to aid in dissipating the heat produced by the die. For example, in the leadframe of FIG. 1, the paddle 12 is often made of metal, and the adhesive 14 is thermally conductive, so that some of the heat generated by the die is conducted to the paddle. The physically separated paddle 12 and leads 16 are held in a desired proximity to each other with a mold compound 20, which forms the exterior of the I.C. package 22 (not shown in FIG. 1b for clarity). When heat is generated by I.C. die 10, it is conducted to the paddle as noted above, and then to the leads 16 through the mold compound 20. Unfortunately, however, molding compounds in common use have a very low thermal conductivity. This increases the thermal resistance between the die and the leads, and limits the amount of heat that can be dissipated by the die. The limited heat dissipation capabilities of such a package in turn limit the power that can be consumed by the I.C. die, as well as the uses to which the die can be put. Poor heat dissipation can also accelerate the failure rate of the die's circuitry. Furthermore, the spacing between the paddle and the leads necessarily limits the size of the die that can be accommodated in a standard package size.